Identification of a VPS13A founder mutation in French Canadian families with chorea-acanthocytosis

Case report: Misdiagnosed orolingual dyskinesia as a consequence of seizures in a chorea-acanthocytosis patient with a novel VPS13A variation from a family with consanguineous marriage

Chorea-acanthocytosis (ChAc) is a rare autosomal recessive inherited syndrome with heterogeneous symptoms, which makes it a challenge for early diagnosis. The mutation of VPS13A is considered intimately related to the pathogenesis of ChAc. To date, diverse mutation patterns of VPS13A, consisting of missense, nonsense, and frameshift mutations, have been reported. In this study, we first report a clinical case that was misdiagnosed as epilepsy due to recurrent seizures accompanied by tongue bite for 9 months, which was not rectified until seizures were controlled and involuntary orolingual movements with awareness became prominent and were confirmed to be orolingual dyskinesia. The patient was eventually diagnosed as ChAc based on whole-exome sequencing revealing novel homozygous c.2061dup (frameshift mutation) and c.6796A > T dual mutations in VPS13A. The patient from a family with consanguineous marriage manifested epileptic seizures at onset, including both generalized tonic-clonic seizures and absence but normal long-term electroencephalography, and gradually developed orofacial dyskinesia, including involuntary tongue protrusion, tongue biting and ulcers, involuntary open jaws, occasionally frequent eye blinks, and head swings. The first test of the peripheral blood smear was negative, and repeated checks confirmed an elevated percentage of acanthocytes by 15-21.3%. Structural brain MRI indicated a mildly swollen left hippocampus and parahippocampal gyrus and a progressively decreased volume of the bilateral hippocampus 1 year later, along with atrophy of the head of the caudate nucleus but no progression in 1 year. We deeply analyzed the reasons for long-term misdiagnosis in an effort to achieve a more comprehensive understanding of ChAc, thus facilitating early diagnosis and treatment in future clinical practice.

Two case reports of chorea-acanthocytosis and review of literature

BACKGROUND

Chorea-acanthocytosis (ChAc), as the most common subtype of neuroacanthocytosis syndrome, is characterized by the presence of acanthocytes and neurological symptoms. It is thought to be caused by the VPS13A (vacuolar protein sorting-associated protein 13A) mutations. This article reports two confirmed cases of ChAc and summarizes some suggestive features, which provide direction for the diagnosis and treatment of acanthocytosis in the future.

CASE PRESENTATION

Here, we present two cases of ChAc diagnosed based on typical clinical symptoms, neuroimaging features, genetic findings of VPS13A, and response to the symptomatic treatment.

CONCLUSIONS

Chorea-acanthocytosis is a rare neurodegenerative disease with various early clinical manifestations. The final diagnosis of the ChAc can be established by either genetic analysis or protein expression by Western blotting. Supportive treatments and nursing are helpful to improve the quality of the patient's life. Nevertheless, it is imperative to investigate the impact of neuroimaging and neuropathological diagnosis in a larger group of ChAc in future studies.

Mutations in VPS13D lead to a new recessive ataxia with spasticity and mitochondrial defects

OBJECTIVE

To identify novel causes of recessive ataxias, including spinocerebellar ataxia with saccadic intrusions, spastic ataxias, and spastic paraplegia.

METHODS

In an international collaboration, we independently performed exome sequencing in 7 families with recessive ataxia and/or spastic paraplegia. To evaluate the role of VPS13D mutations, we evaluated a Drosophila knockout model and investigated mitochondrial function in patient-derived fibroblast cultures.

RESULTS

Exome sequencing identified compound heterozygous mutations in VPS13D on chromosome 1p36 in all 7 families. This included a large family with 5 affected siblings with spinocerebellar ataxia with saccadic intrusions (SCASI), or spinocerebellar ataxia, recessive, type 4 (SCAR4). Linkage to chromosome 1p36 was found in this family with a logarithm of odds score of 3.1. The phenotypic spectrum in our 12 patients was broad. Although most presented with ataxia, additional or predominant spasticity was present in 5 patients. Disease onset ranged from infancy to 39 years, and symptoms were slowly progressive and included loss of independent ambulation in 5. All but 2 patients carried a loss-of-function (nonsense or splice site) mutation on one and a missense mutation on the other allele. Knockdown or removal of Vps13D in Drosophila neurons led to changes in mitochondrial morphology and impairment in mitochondrial distribution along axons. Patient fibroblasts showed altered morphology and functionality including reduced energy production.

INTERPRETATION

Our study demonstrates that compound heterozygous mutations in VPS13D cause movement disorders along the ataxia-spasticity spectrum, making VPS13D the fourth VPS13 paralog involved in neurological disorders. Ann Neurol 2018.

Neuronal Dysfunction in iPSC-Derived Medium Spiny Neurons from Chorea-Acanthocytosis Patients Is Reversed by Src Kinase Inhibition and F-Actin Stabilization

Chorea-acanthocytosis (ChAc) is a fatal neurological disorder characterized by red blood cell acanthocytes and striatal neurodegeneration. Recently, severe cell membrane disturbances based on depolymerized cortical actin and an elevated Lyn kinase activity in erythrocytes from ChAc patients were identified. How this contributes to the mechanism of neurodegeneration is still unknown. To gain insight into the pathophysiology, we established a ChAc patient-derived induced pluripotent stem cell model and an efficient differentiation protocol providing a large population of human striatal medium spiny neurons (MSNs), the main target of neurodegeneration in ChAc. Patient-derived MSNs displayed enhanced neurite outgrowth and ramification, whereas synaptic density was similar to controls. Electrophysiological analysis revealed a pathologically elevated synaptic activity in ChAc MSNs. Treatment with the F-actin stabilizer phallacidin or the Src kinase inhibitor PP2 resulted in the significant reduction of disinhibited synaptic currents to healthy control levels, suggesting a Src kinase- and actin-dependent mechanism. This was underlined by increased G/F-actin ratios and elevated Lyn kinase activity in patient-derived MSNs. These data indicate that F-actin stabilization and Src kinase inhibition represent potential therapeutic targets in ChAc that may restore neuronal function.

SIGNIFICANCE STATEMENT

Chorea-acanthocytosis (ChAc) is a fatal neurodegenerative disease without a known cure. To gain pathophysiological insight, we newly established a human in vitro model using skin biopsies from ChAc patients to generate disease-specific induced pluripotent stem cells (iPSCs) and developed an efficient iPSC differentiation protocol providing striatal medium spiny neurons. Using patch-clamp electrophysiology, we detected a pathologically enhanced synaptic activity in ChAc neurons. Healthy control levels of synaptic activity could be restored by treatment of ChAc neurons with the F-actin stabilizer phallacidin and the Src kinase inhibitor PP2. Because Src kinases are involved in bridging the membrane to the actin cytoskeleton by membrane protein phosphorylation, our data suggest an actin-dependent mechanism of this dysfunctional phenotype and potential treatment targets in ChAc.

Brain, blood, and iron: perspectives on the roles of erythrocytes and iron in neurodegeneration

The terms "neuroacanthocytosis" (NA) and "neurodegeneration with brain iron accumulation" (NBIA) both refer to groups of genetically heterogeneous disorders, classified together due to similarities of their phenotypic or pathological findings. Even collectively, the disorders that comprise these sets are exceedingly rare and challenging to study. The NBIA disorders are defined by their appearance on brain magnetic resonance imaging, with iron deposition in the basal ganglia. Clinical features vary, but most include a movement disorder. New causative genes are being rapidly identified; however, the mechanisms by which mutations cause iron accumulation and neurodegeneration are not well understood. NA syndromes are also characterized by a progressive movement disorder, accompanied by cognitive and psychiatric features, resulting from mutations in a number of genes whose roles are also basically unknown. An overlapping feature of the two groups, NBIA and NA, is the occurrence of acanthocytes, spiky red cells with a poorly-understood membrane dysfunction. In this review we summarise recent developments in this field, specifically insights into cellular mechanisms and from animal models. Cell membrane research may shed light upon the significance of the erythrocyte abnormality, and upon possible connections between the two sets of disorders. Shared pathophysiologic mechanisms may lead to progress in the understanding of other types of neurodegeneration.

Neuroacanthocytosis syndromes

Neuroacanthocytosis (NA) syndromes are a group of genetically defined diseases characterized by the association of red blood cell acanthocytosis and progressive degeneration of the basal ganglia. NA syndromes are exceptionally rare with an estimated prevalence of less than 1 to 5 per 1'000'000 inhabitants for each disorder. The core NA syndromes include autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome which have a Huntington´s disease-like phenotype consisting of a choreatic movement disorder, psychiatric manifestations and cognitive decline, and additional multi-system features including myopathy and axonal neuropathy. In addition, cardiomyopathy may occur in McLeod syndrome. Acanthocytes are also found in a proportion of patients with autosomal dominant Huntington's disease-like 2, autosomal recessive pantothenate kinase-associated neurodegeneration and several inherited disorders of lipoprotein metabolism, namely abetalipoproteinemia (Bassen-Kornzweig syndrome) and hypobetalipoproteinemia leading to vitamin E malabsorption. The latter disorders are characterized by a peripheral neuropathy and sensory ataxia due to dorsal column degeneration, but movement disorders and cognitive impairment are not present. NA syndromes are caused by disease-specific genetic mutations. The mechanism by which these mutations cause neurodegeneration is not known. The association of the acanthocytic membrane abnormality with selective degeneration of the basal ganglia, however, suggests a common pathogenetic pathway. Laboratory tests include blood smears to detect acanthocytosis and determination of serum creatine kinase. Cerebral magnetic resonance imaging may demonstrate striatal atrophy. Kell and Kx blood group antigens are reduced or absent in McLeod syndrome. Western blot for chorein demonstrates absence of this protein in red blood cells of chorea-acanthocytosis patients. Specific genetic testing is possible in all NA syndromes. Differential diagnoses include Huntington disease and other causes of progressive hyperkinetic movement disorders. There are no curative therapies for NA syndromes. Regular cardiologic studies and avoidance of transfusion complications are mandatory in McLeod syndrome. The hyperkinetic movement disorder may be treated as in Huntington disease. Other symptoms including psychiatric manifestations should be managed in a symptom-oriented manner. NA syndromes have a relentlessly progressive course usually over two to three decades.

Chorea-acanthocytosis genotype in the original critchley kentucky neuroacanthocytosis kindred

OBJECTIVE

To determine the molecular nature of the neurological disease in the seminal family reported by Critchley et al in the 1960s, characterized by a hyperkinetic movement disorder and the appearance of acanthocytosis on peripheral blood smear. The eponym Levine-Critchley syndrome, subsequently termed neuroacanthocytosis, has been applied to symptomatically similar, but genetically distinct, disorders, resulting in clinical and diagnostic confusion.

DESIGN

DNA analysis.

SETTING

Molecular biology research laboratories.

PARTICIPANTS

First- and second-degree relatives of the original Critchley et al proband from Kentucky.

MAIN OUTCOME MEASURES

Mutations in the VPS13A gene.

RESULTS

A mutation was identified in the VPS13A gene, responsible for autosomal recessive chorea-acanthocytosis. Haplotype reconstruction suggested that this mutation was homozygous in the proband.

CONCLUSION

These findings strongly support the diagnosis of chorea-acanthocytosis as the disorder described in the original report.

Novel pathogenic mutations and copy number variations in the VPS13A gene in patients with chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is a rare autosomal recessive neurodegenerative disorder caused by loss of function mutations in the vacuolar protein sorting 13 homolog A (VPS13A) gene that encodes chorein. It is characterized by adult-onset chorea, peripheral acanthocytes, and neuropsychiatric symptoms. In the present study, we performed a comprehensive mutation screen, including sequencing and copy number variation (CNV) analysis, of the VPS13A gene in ChAc patients. All 73 exons and flanking regions of VPS13A were sequenced in 35 patients diagnosed with ChAc. To detect CNVs, we also performed real-time quantitative PCR and long-range PCR analyses for the VPS13A gene on patients in whom only a single heterozygous mutation was detected. We identified 36 pathogenic mutations, 20 of which were previously unreported, including two novel CNVs. In addition, we investigated the expression of chorein in 16 patients by Western blotting of erythrocyte ghosts. This demonstrated the complete absence of chorein in patients with pathogenic mutations. This comprehensive screen provides an accurate and useful method for the molecular diagnosis of ChAc.

Characteristic head drops and axial extension in advanced chorea-acanthocytosis

Chorea-acanthocytosis is a rare autosomal recessive neurodegenerative disorder with a complex clinical presentation comprising of a mixed movement disorder (mostly chorea and dystonia), seizures, neuropathy and myopathy, autonomic features as well as dementia and psychiatric features. Because the differential diagnosis is wide, clinical clues and red flags are important. We report here our observation of characteristic neck and trunk flexion and extension spasms in four cases with advanced chorea-acanthocytosis.

Adolescent obsessive compulsive disorder heralding chorea-acanthocytosis

We describe one male and one female patient who each developed childhood/adolescent obsessive-compulsive disorder as a prelude to the development of a typical picture of chorea-acanthocytosis (ChAc). In each patient, the caudate nucleus showed dramatic atrophy. The role of the caudate in compulsive phenomena, and the predilection for neurological disorders with onset in adolescence to present as major mental illness, is discussed. On the basis of the current evidence and previous findings, we suggest that ChAc can be understood as a disorder whose clinical presentation reflects an interaction between the disease process and the individual's neurodevelopmental stage with both initial interrupted neurodevelopment, and supervening neurodegeneration.

Primary skeletal muscle involvement in chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is a hereditary disease characterized by involuntary movements and amyotrophy with elevation of serum creatine kinase. Although skeletal muscle involvement in ChAc has been suggested, the mechanism remains unclear. To investigate chorein abnormalities of the skeletal muscles of ChAc patients with an apparently heterozygous VPS13A mutation compared with those of other hereditary choreic diseases, we performed histological and immunohistochemical studies of the skeletal muscles from 3 ChAc, 1 Huntington's disease (HD), 1 McLeod syndrome (MLS), and 1 normal control (NC) with 2 originally generated anti-chorein antibodies. Chorein immunoreactivities in HD, MLS, and NC were found linearly along the sarcolemma and appeared as speckles in the sarcoplasma, but those in ChAc were uneven and discontinuous along the sarcolemmas and increased in the sarcoplasma especially in type I fibers. This histological observation suggests chorein abnormalities of skeletal muscles might be associated with primary involvement of skeletal muscles in this disorder.

When intracellular logistics fails--genetic defects in membrane trafficking

The number of human genetic disorders shown to be due to defects in membrane trafficking has greatly increased during the past five years. Defects have been identified in components involved in sorting of cargo into transport carriers, vesicle budding and scission, movement of vesicles along cytoskeletal tracks, as well as in vesicle tethering, docking and fusion at the target membrane. The nervous system is extremely sensitive to such disturbances of the membrane trafficking machinery, and the majority of these disorders display neurological defects--particularly diseases affecting the motility of transport carriers along cytoskeletal tracks. In several disorders, defects in a component that represents a fundamental part of the trafficking machinery fail to cause global transport defects but result in symptoms limited to specific cell types and transport events; this apparently reflects the redundancy of the transport apparatus. In groups of closely related diseases such as Hermansky-Pudlak and Griscelli syndromes, identification of the underlying gene defects has revealed groups of genes in which mutations lead to similar phenotypic consequences. New functionally linked trafficking components and regulatory mechanisms have thus been discovered. Studies of the gene defects in trafficking disorders therefore not only open avenues for new therapeutic approaches but also significantly contribute to our knowledge of the fundamental mechanisms of intracellular membrane transport.

Head of the caudate nucleus is most vulnerable in chorea-acanthocytosis: a voxel-based morphometry study

Chorea-acanthocytosis (ChAc; OMIM 200150) is a rare autosomal recessive disease with dysfunction of the erythrocyte membrane, presenting with acanthocytes and neurological manifestations characterized by progressive hyperkinesias (chorea, dystonia) and neuropsychological impairment. Damage to the basal ganglia was described previously in neuropathological and neuroimaging investigations. We analyzed high-resolution MRI of six ChAc patients with mutations in the VPS13A gene (median age, 37 years; mean time since clinical onset, 13 years) with respect to regional atrophy by use of the observer-independent technique of voxel-based morphometry in comparison to 15 age-matched healthy controls. Additionally, global brain atrophy was determined using the standardized brain parenchymal fraction (BPF) method. A robust regional reduction of gray matter density was observed in the head of the caudate nucleus bilaterally and was nearly symmetrical (P < 0.001, corrected for small volumes). No additional gray matter changes were found. In the BPF analysis, there was no significant global brain atrophy. The predilection of atrophy in the head of the caudate nucleus, as suggested by our results, argues for a particular vulnerability of this part of the striatum in ChAc and is in agreement with pronounced neuropsychological disturbances that are thought to rely on these regions.

Brain-specific transcript variants of 5′ and 3′ ends of mouse VPS13A and VPS13C

Mutations in vacuolar protein sorting 13A (VPS13A) gene are responsible for chorea-acanthocytosis (ChAc). We previously determined the full-length sequence and exon-intron structure of mouse VPS13A and generated a ChAc model mouse by using the gene targeting technique. In the process, we found diverse 5' and 3' transcript variants. Since ChAc is a rare neurodegenerative disorder, the mouse model should be useful for investigation of ChAc molecular pathogenesis, and the model's brain specific variants of VPS13A will be indispensable in these investigations. In the present study, we investigated mouse VPS13A transcript variants. We found brain-specific variants of mouse VPS13A, which may be involved in the brain-specific pathology of ChAc. In addition, we identified for the first time mouse VPS13C cDNA sequences and brain-specific variants of VPS13C.

Developments in neuroacanthocytosis: Expanding the spectrum of choreatic syndromes

As with other neurodegenerative disorders, research into the group of diseases known under the umbrella term of "neuroacanthocytosis" has greatly benefited from the identification of causative genes. The distinct and unifying aspect of these disorders is the presence of thorny deformations of circulating erythrocytes. This may be due to abnormal properties of red cell membranes, which could lead to insights into mechanisms of neurodegeneration. Research approaches in this field, in addition to examining functions and protein interactions of the affected proteins with particular respect to neurons, have also drawn upon the expertise of hematologists and red cell membrane biologists. In this article, recent developments in the field are presented.